Industrial measuring instruments such as flow or level meters serve to collect data such as volume or mass flow or fill level values. In general, however, they do not provide a direct read-out of the value of interest, i.e. of the volume or mass flow or of the fill level. Instead, the acquired data represent information for instance on the lift height of a float in a float-type flow meter, the intensity of an induced current in a magnetoinductive flow meter or the run time of a radar signal in a radar-type level meter. In fact, if for instance in a float-type flow meter, the lift height of the float is detected via a trailing magnet, then even the lift height determination of the float is indirect only, i.e. in the form of flux-density information that must then be correlated with the volume flow concerned.
The data thus acquired must therefore be processed, i.e. converted in order to yield a signal that indicates the actual value of interest such as the flow rate or the fill level. This requires linearization of the collected initial data on the basis of predefined calibration parameters. It follows that prior to any industrial application, the measuring instrument concerned must be calibrated based on the parameters predefined for the linearization so that in an actual measuring operation, each directly acquired datum can be unambiguously translated into an appropriate flow or level value.
In the case of the flow and level meters referred to above as examples, the flow or level value thus measured is fed to a display or output device. Typical displays are of an analog or digital design and are often mounted directly on the measuring instrument. But then again, it is often desirable to display and/or further process the measured values at a remote location. To that effect, the measuring instrument is usually equipped with an interface through which the measuring instrument outputs the measured data, typically in the form of a test voltage or test current. The type of interface and the manner in which the data are transferred are generally defined by the protocol or bus system used. Examples include the signal transmission, as a current signal of between 4 and 20 mA, via a two-wire circuit, a HART, PROFIBUS, FOUNDATION FIELDBUS, etc.
There is a problem in that a measuring instrument is usually equipped with only one type of interface for the data transmission, so that a change of the system in which the measuring instrument is integrated requires either a complete replacement of the measuring instrument or, if the measuring instrument is modified with a new interface, at least one recalibration. That is time-consuming and expensive.